I can publish my VB 2008 ASP.Net website and run it without any problem. I can also run the website in debug mode and view the charts without any problem. But if I copy the website to another directory on my network, I get the "Unable to write chart image files at given file path" error (A generic error occurred in GDI+).
Why can I debug one copy of my website without error, whereas the exact same website, copied to another directory, gives the error when I try to run in debug mode?
I erased the web app from the new drive, and then created a new web project on that drive. Then I copied the web app from its original location to the newly created location, and the debugging worked fine.
I guess you can't just simply copy the web app from one directory to another. Anyway, problem solved.